XF 1.4 Fatal error: 'XenForo_ViewAdmin_Base' -Cannot Login to Admin

Hi,
just few minutes before, i logged into forum admin panel from my mobile,
everything was working fine, then just before i tried logging into forum admin panel in my PC,
i got this error, now everywhere i am receiving the same
just want to mention that, i migrated my forum to VPS last week,

this never happened before,

I already browsed through forum,
somebody suggested truncating the session table
will it work in this case?
can i do this via phpmyadmin??

This is the error, - Fatal error: Class 'XenForo_ViewAdmin_Base' not found in /home/rbharathi820/public_html/forum/library/XenForo/ViewAdmin/Login/Form.php on line 4

Hi Brogan,
Thank you for quick response,
forum was working fine for last 10 days after migration.
today only i am facing this error,
anyway i tried re uploading that file,
but the problem is still there!!

Yes Brogan, i did everything on admin panel, for the past ten days.
i think something happening with server side, so, will speak about this, Thanks a lot for your quick support.
Being happy XF customer.